Paying for something "out of your own pocket" means that you pay for it yourself, rather than having it paid for by someone else. You especially use "out of ___ own pocket" when:
- someone pays for something that should have been payed for by someone else (like in the example above)
- someone pays for something that's really expensive and hard to afford. For example:
A few notes: people can only pay out of their own pocket. It doesn't make sense to talk about paying out of someone else's pocket. And it's always singular "pocket", not "pockets".